1. Field of the Invention
The invention concerns the field of electrographic reproduction, and specifically, apparatus and a process whereby the pressure member involved in fusing the image to the support material or copy sheet is kept clean of extraneous debris which commonly builds up from the copy sheets contacted by the pressure member.
2. State of the Prior Art
Electrographic imaging and developing processes, e.g., electrophotographic imaging processes and techniques, have been extensively described in both the patent and other literature, for example, U.S. Pat. Nos. 2,221,776, issued Nov. 19, 1940; 2,277,013, issued Mar. 17, 1942; 2,297,691, issued Oct. 6, 1942; 2,357,809, issued Sept. 12, 1944; 2,551,582, issued May 8, 1951; 2,825,814, issued Mar. 4, 1958; 2,833,648, issued May 6, 1958; 3,220,324, issued Nov. 30, 1965; 3,220,831, issued Nov. 30, 1965; 2,330,822, issued Nov. 30, 1965; Research Disclosure, Vol. 109, May 1973, publication 10938; and many others. Generally, these processes have in common the steps of forming a latent electrostatic charge image on an insulating electrographic element. the electrostatic latent image is then rendered visible by a development step in which the charged surface of the electrographic element is brought into contact with a suitable developer. The developed visible image relies upon an imagewise distribution of an opaque material, commonly known as a toner, usually deposited in a dry particle form. Electrostatic transfer of such toner particles to the support material, and their fusion by the application of heat, are well-known. Typically, the fixing or fusing step may be achieved by a pair of heated, counter-rotating rollers, commonly known as fusing rollers. Construction of such rollers, and methods of heating the same, are discussed in detail in Product Licensing Index, Vol. 99, July 1972, Publication No. 9944, pages 72 and 73.
The fusing rollers, by virtue of their repeated contact with the copy sheet, tend to build up debris in the form of paper fibers, lint and the like from the copy sheet, particularly in the areas of the sheet which do not bear a toner image. Thus, multiple copies of the same original cause the same non-imaged areas of the copy sheet to contact the rollers. Unless cleaning means are introduced, the continuous build-up of debris finally results in significant amounts of debris being transferred to the fusing roller so as to mask its required release characteristics.
To clean the rollers, it has been conventional to cover the roller initially with an abhesive surface, as explained in the aforesaid Product Licensing Index. However, these coverings are not only expensive to fabricate, they also are inherently heat insulative, requiring further treatment with materials of high heat conductivity in order to permit proper fusing by the rollers. Still other solutions of the problem have incorporated cleaning or release liquids either alone or in combination with abhesive covers, silicone oils being an example. Such liquids have proven to be effective only for short and generally unpredictable duration. Further, by being in liquid form they of necessity are characterized by handling problems, and under high heat conditions they can cause degradation of the abhesive layer. Typical examples of the use of release liquids and/or abhesive coatings can be found in U.S. Pat. Nos. 3,268,351, issued Aug. 23, 1966; 3,324,791, issued June 13, 1967 and 3,331,592, issued July 18, 1967.
Other publications pertinent to the background of cleaning apparatus for portions of electrographic copiers can be found in the following sources:
U.S. Pat. Nos. 3,411,932, issued on Nov. 19, 1968; 3,526,457, issued Sept. 1, 1970; 3,615,397, issued Oct. 26, 1971; 3,624,858, issued Dec. 7, 1971; 3,673,632, issued July 4, 1972; 3,686,035, issued Aug. 22, 1972; and Product Licensing Index, Vol. 94, February 1972, Publication No. 9406, pages 48-49.
Still another approach has been to run plain paper through the rollers at a slow rate and without developing material, as shown for example in U.S. Pat. No. 3,706,491. However, such an approach cleans only excess tone from the rollers, and not fibrous material. In fact, such a technique aggravates the problem of lint contamination. A different solution for the removal of toner, but not fibers, has involved the use of triboelectric cleaning granules impinged against the unwanted toner, such as is taught by U.S. Pat. No. 3,424,615 and U.S. Pat. No. 3,654,901. However, this process concerns only the cleaning of the photoconductive plate, and as with the case of plain paper, is in any case insufficient to clean paper fibers.
Resins of course have been coated on non-imaging papers for protective reasons rather than as a cleaner, and the following U.S. Patents are representative of such technology: U.S. Pat. Nos. 3,479,213; 3,112,985; 3,110,618; 2,790,735; 2,583,274; 2,434,106; 2,406,454 and 2,125,527. Liquid dispersions containing resins have also been deposited over unfused image powder on copy sheets or support material, of which examples can be found in U.S. Pat. No. 3,779,748, issued Dec. 18, 1973. However, such dispersions were designed for the properties given to the final copy, and are limited by the handling problems characteristic of all liquids.